Method and apparatus for electrical precipitations



June 12, 1934. w. DEUTSCH 1,962,555

METHQD AND APPARATUS FOR ELECTRICAL PRECIPITATION Filed oct 8; 1932 ATTOR/VE J Patented June 12, 1934 UNITED STATES PATENT OFFICE MET-HODWalther Deutsch, Frankfort- AND APPARATUS FOR ELECTRICAL PRECIPITATIONSon-theMain, Ger- Company, Los Angeles,

California 4 Claims.

This invention relates to the electrical precipitation of suspendedparticles from gases.

The principal object of the invention is to provide a novel andadvantageous method and ap- 5 paratus for effecting such electricalprecipitation.

With very few exceptions, the apparatus heretofore known for electrical,precipitation comprises two essential parts or elements, namely,discharge electrodes and collecting electrodes, which perform certaindefinite functions. The relatively great curvature of the surface of thedischarge electrodes, which usually consist of points, thin wires or thelike, causes a corona discharge to occur upon application of a. highpotential difference between these electrodes and the collectingelectrodes, and this corona discharge serves to produce ions in the gas,for electrically charging the suspended particles.

The collecting electrodes not only'serve as opposing electrode meanswhereby high potential for ionization and the, necessary for preclpitation of the charged particles may be maintained, but also providedepositing surfaces for the precipitated material.

It has been proposed to use various materials in the dischargeelectrodes. For example, glass covered metal wires may be used toprovide more uniform distribution of corona, or rods having surfacescovered with points or with thin threads or filaments of non-conductingmaterial. It has also been proposed to use rods over whose surface aconducting liquid. such as water, is caused to flow. Under the action ofan electric field the water film is caused to form into small dropletsat whose surface an eifective corona discharge is produced. However, theknown forms of discharge electrodes which are mosteffective forionization, such as thin wires or line points, are ordinarily fragileand have relatively little strength or corrosion resistance, and forthis reason larger elements such as rods, used, in spite of the factthat they less efficient as sources of corona are ordinarily aresomewhat discharge. It

is also sometimes undesirable to introduce moisture into theprecipitator, orsuch moisture introduction may-be impossible, as in thetreatment of gases at high temperature which would cause immediateevaporation of the liquid.

A particular object of the present invention, therefore,'is to provide asource of corona dis charge or ionization, for use as dischargeelectrode means in electrical precip will ofier relatively sharp surfacecorrespondingly high corona pr which is not open to objection onitators, which curvature" and oduction, an

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low mechanical strength or corrosion resistance,

It is known that the path of the spark constitutes a linear conductor ofextremely small ra dius of curvature. If a spark is produced andmaintained between two electrodes, and a strong unidirectional electricfield is maintained be tween these electrodes and a third electrodewhich is disposed, for example, parallel to the path of said spark, aunidirectional corona will occur at or adjacent the spark itself, due tothe 5 small radius of curvature of the conductive path thereof. Thecorona is thus produced without necessitating the provision of a thinwire or other discharging member between the two firstnamed electrodes,and the conducting path of the spark itself serves as the ionizing ordischarge electrode, while the third electrode serves as a collectingelectrode.

The action which takes place with such an arrangement may-be describedas follows: The unidirectional field serves to displace the sparksomewhat from its normal position between the two first-mentionedelectrodes, toward the third electrode, thus substantially eliminatingany screening effect of the electrodes between which. the spark ismaintained, and permitting corona discharge to be maintained throughoutsubstantially the entire length of the spark. Further more, the electricwind which is created after the corona discharge is started serves tofurther dis- $5 tort the spark path away from the screening action ofthe sparking electrodes and provide still more favorable conditions forcorona discharge,

The spark whose conducting path is utilized as a discharge electrode maybe produced by either alternating or unidirectional current, and thesparking electrodes may be placed sumciently close together so that apotential. of a few thousand volts is sufficient to produce a sparktherebetween. As it is more advantageous to produce a number of fine orthread-like sparks between these two electrodes, rather than a heavierluminous arc, it is preferable to limit the current between theseelectrodes by insertion of a relatively high reslstance in the circuitof such current flow. This 1 a resistance may advantageously be providedover insulating potential two auxiliary or sparking electrodes isindependent of the discharge produced between these auxiliary electrodesand the third or collecting electrode by the unidirectional coronaproduced at the surface of the spark orsparks. The corona is producedsolely by the unidirectional field maintained between the auxiliaryelectrodes and the collecting electrode, and the ions which are utilizedto charge the particles are derived exclusively from this unidirectionalcorona, while the discharge between the auxiliary electrodes proceedsentirely undisturbed. All electrons and ions emanating from one of theauxiliary electrodes arrive at the opposite auxiliary electrode and viceversa. If,- for example, an alternating potential is maintained betweenthe auxiliary electrodes, the alternate emanation of electrons and ionsfrom these two electrodes, due to the alternating field, takes place inthe same manner, whether or not the unidirectional field is alsomaintained. The sole function of this alternating discharge is toproduce a narrow conducting path which serves to replace the dischargeelectrodes ordinarily employed.

It will be apparent that the method of the present invention cannot besafely used in the treatment of explosive or combustible mixtures ofgases,

and suspended material.

The accompanying drawing illustrates the method and apparatus of thisinvention, and referring thereto:

Fig. 1 is a diagrammatic representation of one type of electrodes whichmay be used, together with means for maintaining the necessaryelectrical potentials therebetween.

Figs. 2 and 3 are diagrammatic representations showing modified forms ofelectrodes.

-Referring to the drawing, and particularly to Fig. 1, the auxiliaryspark gap electrodes are shown at 1 and 2. Said electrodes may be formedas relatively massive bodies, such as spheres or rods, and the surfaceof either or both of said electrodes may, if desired, be covered withsuitable material, such as glass. Said electrodes are connected to asource of electrical potential sufiicient to maintain a spark dischargetherebetween, as indicated at 3. An alternating may be used for thispurpose, and the electrodes 1 and 2 are shown as connected by wires 4and 5 to the opposite terminals of a transformer 6.

A collecting electrode 7 of extended area is pro-- vided, the surface ofwhich is preferably substantially parallel to the path of the sparkdischarge between the electrodes 1 and 2. A unidirectional potential ismaintained between the collecting electrode 7 and one of the electrodes1 or 2. For this purpose, the electrode 7 is shown as connected bythrough a rectifying device 10 and wire 11 to electrode 1.

The path of the spark 3 produced between electrodes 1 and 2 isrelatively thin and'serves as a discharge electrode. It will beunderstood, however, that the spark discharge may consistr of one or aplurality of narrow spark paths, and that wire 8 to one terminal oftrans' former 9, the other terminal of which is connected rectifier 10serves to maintain a suificiently high electrical field between thisdischarge electrode and the collecting electrode to cause a coronadischarge or ionization to occur from the path of the spark toward thecollecting electrode, as indicated for example at 12. Due to therelatively large cross-section of electrodes 1 and 2, as compared to thespark path, such corona discharge occurs substantially wholly from saidspark path. If gas containing suspended particles is then passed throughthe space between the spark path 3 and the collecting electrode 7, thesuspended particles will become electrically charged by ions produced bysaid corona, and the charged particles will be precipitated upon thecollecting electrode by the electrical field between said spark path andcollecting electrode.

As above stated, it may be advantageous to insert a relatively highresistance in series with the spark gap electrodes 1 and 2. Thisresistance may be provided, for example, by providing a covering orcoating of insulating or high resistance material over the surface ofboth of said electrodes, as shown at In and 2a in Fig. 2, or over thesurface of one of said electrodes as shown at 1:1 in Fig. 3.

I claim:

l. The method of electrical precipitation which comprises m'ainiainingan electric spark across a path between two oppositely charged electrodemembers, maintaining a unidirectional electrical potential diiferencebetween said spark and a third electrode of exlended surfacesubstantially parallel to the path of said spark, said potential beingsufiicient to cause the narrow conducting whereby corona dischargeoccurs substantially wholly from said spark gap toward said thirdelectrode, and passing gas containing suspended material through theelectrical field between said spark path and said third electrode.

2. An apparatus for electrical precipitation comprising two oppositelycharged electrode members, means for maintaining an electrical potentialbetween said electrode members sufiicient to produce a spark dischargetherebetween, a third electrode of extended surface positionedsubstantially parallel to the path of said spark discharge andat nopoint substantially closer to said firstnamed electrode members than tothe path of said spark discharge, means for maintaining a unidirectionalelectrical potential between said third electrode and the circuitincluding said first-v named electrodes sufiicient to cause coronadischarge to occur from said spark toward said third electrode, saidfirst-named elecirodes being of relatively large cross-section comparedto said spark path whereby said corona discharge occurs substantiallywholly from said spark path, and means for passing gas containingsuspended material between said spark path and said third electrode.

3. An apparatus as set forth in claim 2 and also comprising resistancemeans connected in series with said two first-named electrodes.

4. An apparatus as set forth in claim 2, in which at least one of saidtwo first-named electrodes is covered with material of high resistance.

WALTHER DEUTSCH.

